Research in Malawi finds girls who receive regular payments are able to resist attentions of older men and avoid infection.The randomised controlled trial was carried out in one of the poorest parts ofMalawi. Photograph: Martin Godwin

Regular small cash payments to girls and young women can enable them to resist the attentions of older men and avoid HIV infection, according to a new study.

Girls and young women are at the greatest risk of HIV infection in endemic countries. In sub-SaharanAfrica, between a quarter and a third have the virus by the time they reach their early 20s.

But educating girls about risks and promoting condom use has had little impact in countries where they are struggling with poor education, low status and poverty, and where older men with money offer one of the few ways out of financial difficulties.

A team of researchers from the World Bank, University of California at San Diego and GeorgeWashington University in the US carried out a randomised controlled trial in Malawi to find out whether monthly payments to schoolgirls and their families would help change the girls' behaviour and safeguard their health.

They recruited nearly 1,300 young women, aged from 13 to 22, who were enrolled in school in the Zomba district of southern Malawi – an area of poverty, low school enrolment and high HIV prevalence.The young women were randomly assigned, according to where they lived, either to receive between $1 and £5 a month, with their families given between $4 and $10 a month, or to get nothing. At the end of 18 months, the girls were tested for HIV and herpes infection.